Choose the correct answer from the four options given below:
A muscular wall is absent in:
Topic: Capillary structure
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Pick an option and check your answer. The full worked answer is below either way.
Answer
(a) Capillary.
A CAPILLARY has NO muscular wall at all. Its wall is a single layer of flattened cells — one cell thick.
WHY IT MUST BE SO: the capillary is where EXCHANGE happens. Oxygen, nutrients and wastes must diffuse between the blood and the tissue fluid, and a thick muscular wall would prevent it. The extreme thinness is the whole point of the structure.
All the others have muscle in their walls, though in differing amounts: arterioles most, then venules and veins.
THE PRINCIPLE that recurs throughout biology: wherever exchange occurs, the surface is THIN and the area LARGE. The same design appears in the alveoli of the lungs, the villi of the intestine and the root hairs of a plant.
Capillary.